Short stroking question

[Swstock]

I bought an upper second hand and it worked great.

It was a Centurion 16" mid length barrel cut down with a pinned and welded compensator to make it 16OAL. It had a Rainier BCG and upper receiver. It ran flawlessly in a carbine class.

I swapped the receiver and BCG for Centurion stuff to make it a single brand upper. I took it to a range, re-zerod it and it seemed fine. I used about 50 rounds.

A week later, Im back in another class and its short stroking. Luckily, I was able to swap uppers and had no interruption of training.

Upper
Former 16" cut to 14.5" Centurion CHF mid length barrel with pinned Battlecomp brake
Centurion receiver
Centurion BCG
Centurion quad rail

Ammo: MEN 56gr 5.56

I tried 2 different lowers that I know work fine with all of my other uppers and the problem wasn't resolved.

They BOTH have Geissele super 42 braided springs and H1 buffers and run well with all of my other uppers.

The gas tube WAS sealed when it was running fine. When I put it back together, I did not seal it. Since I had this issue, I took it back apart and sealed it with blue locktite. Hopefully this works.

My questions are: Could gas tube sealant actually solve this or should I keep digging before I hit the range again? I feel like IF the answer is yes, then there isnt much margin of error preventing this from happening again. Also, I don't normally seal gas tubes into the gas block and don't have issues with other builds. Is it luck? Most others are 16"mids but I do have another 15ish" mid with a pinned and welded brakes that runs fine. This is 14.5" so dwell time is a little shorter than the 16s.

If I go to a carbine buffer, am I just putting a bandaid on this and not identifying or solving the problem? Did it just need to be cleaned before range visits? My round count was low and it only sat for about a week.

Thoughts?

[Clint]

Was the gas block moved/removed during the rebuild?

The Centurion BCG should be GTG, but has it been verified or swapped out to eliminate that variable?

[Swstock]

Was the gas block moved/removed during the rebuild?

The Centurion BCG should be GTG, but has it been verified or swapped out to eliminate that variable?

Thanks for asking. I just came back to mention that I did not remove the gas block. That is pinned and sealed so wasnt worth trying to remove.

When I go back, ill bring a few spare BCGs to try.

[lonestardiver]

<edited comment after re-reading OP>

[MistWolf]

Basic checklist when an AR starts short stroking-

First, check to make sure it locks back when operating the charging handle manually

Second, test your AR using full power 5.56

Third, check for leaks blockages and misaligned parts in the gas system

Fourth, don't waste your time playing with lighter buffers & springs. A properly gassed AR wil be fully functional with a standard spring and an H2 buffer, using full power ammo. Palmetto kits ship with a carbine weight buffer, which is too light

Fifth, when (not if) you start getting empty cases caught in the action, replace the extractor spring with one from Colt or Sprinco- no O ring! Accept no substitutes

I posted this in another thread-

I started having short stroking problems on a high mileage suppressed 11.5" upper.

The BCG related discrepancies were as follows-
- worn gas rings. Installed new gas rings
- leaky gas key. Removed gas key. Cleaned mating surfaces, reinstalled key & staked
- gas tube worn where it fit into the gas key. Installed new gas tube

[Dr. Bullseye]

Looking at MistWolf's post, I would start right here

"They BOTH have Geissele super 42 braided springs and H1 buffers and run well with all of my other uppers."

Go back to the closest thing you can find to mil spec for this rifle and 556 ammo, then test again, then check the rings if still a problem.

[Swstock]

Looking at MistWolf's post, I would start right here

"They BOTH have Geissele super 42 braided springs and H1 buffers and run well with all of my other uppers."

Go back to the closest thing you can find to mil spec for this rifle and 556 ammo, then test again, then check the rings if still a problem.

Its an upper that i use across a few different lowers. If i have to build a lower with a carbine buffer, i will. I just don't want to use a carbine buffer to mask the actual problem.

If a dozen uppers with fine across those lowers, then I want this one to also...unless there is a reasonable explanation.

MistWolf says the lighter buffer isnt the answer and these should run H2 buffers. I just want to make sure it works with an H1. That statement also tells me to keep looking.

I really want to know if gas tube leakage at the gas block could make a noticeable difference. I feel like a small amount is normal. Is a sealant there mandatory? Is there a chance that that 1 thing could have been the problem?

Is a 14.5 mid just to soft for an H1 buffer? This is my second and the first was fine so Im leaning toward no.

I may not figure this out until i swap carriers at the range.

[Dr. Bullseye]

You have so many variables. You say you have run this upper with other lowers and then you want to know if it is a gas tube leak issue. Did you have this issue with the other lowers? If not, you have variables in the configuration under discussion that you have to narrow down and check one by one in order to solve the problem. Am I wrong???

[Swstock]

You have so many variables. You say you have run this upper with other lowers and then you want to know if it is a gas tube leak issue. Did you have this issue with the other lowers? If not, you have variables in the configuration under discussion that you have to narrow down and check one by one in order to solve the problem. Am I wrong???

It works with neither lower now. It ran fine before swapped receivers and the BCG.

The other lowers work with all of my uppers. The lower configurations are the same from a buffer perspective. I think im gonna have to take it to the range and see if its fixed by sealing that small at the gas tube. If not, ill try a different bcg and see what happens.

[Hulkstr8]

I'm not easily keeping track of what you've changed around.

Have you tried dropping butting in a heavier buffer (I hate the Super 42 ftw). Check the gas tube for damage?